JPH08176034A - Synthesis of methanol - Google Patents

Abstract

PURPOSE: To synthesize methanol in higher yield, as compared with a conventional method from a low-grade hydrogen gas having low hydrogen content, e.g. a plant off gas as a hydrogen source and carbon dioxide. CONSTITUTION: This method for synthesizing methanol comprises providing (a) a reactional step for reacting a raw material gas mixture containing carbon dioxide and hydrogen in the presence of a catalyst obtained by supporting at least one kind of metal selected from Ni, Fe, Co, Ru, Rh, Pt and Pd of the group VIII of the periodic table and Mo and W of the group VI of the periodic table onto a carrier comprising a complex of an oxide of a metal selected from either one group of a metal group belonging to the group IIIb of the periodic table and a metal group belonging to the group IVa or a metal each selected from both groups with zinc oxide or a carrier consisting of only zinc oxide and (b) a reactional step for synthesizing methanol from hydrogenation reaction.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for synthesizing methanol, and more particularly to a method for economically producing methanol from carbon dioxide and a low-grade hydrogen-containing gas.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of conservation of the global environment and reuse of resources, research has been conducted on the practical application of a reaction in which carbon dioxide is used as a raw material to obtain a useful product in order to immobilize and recycle carbon dioxide. Has been done. One of them is liquid fuel,
Studies have been conducted to synthesize methanol from carbon dioxide, which has a wide range of uses as a raw material for the chemical industry such as methyl tertiary butyl ether (MTBE), aldehydes, alkylbenzenes, ethylene glycol, and methylates. By the way, conventionally, methanol has a mixed gas of carbon monoxide and hydrogen (synthesis gas) as a raw material gas, and carbon monoxide is hydrogenated in the presence of a specific methanol synthesis catalyst, as shown in the following formula (1). It is manufactured by reducing with. CO + 2H ₂ → CH ₃ OH ΔH ₂₉₈ = -90.6 kJ / mol (exothermic) (1) As a catalyst to be used, Cu-ZnO- used at a reaction temperature of 230 to 270 ° C and a reaction pressure of 50 to 100 kg / cm ^2.
Three-way catalysts such as Al ₂ O ₃ have been known since the 1960s (for example, C ₁ chemistry, Catalysis Society, edited by Kodansha (1984)).

On the other hand, as a method for synthesizing methanol from carbon dioxide and hydrogen, a conventional methanol synthesizing catalyst for producing methanol from water gas in which carbon monoxide and hydrogen are mixed in a ratio of 1: 3 is used as it is as follows. A method of synthesizing methanol by carrying out the reaction of formula (2) has been proposed. CO ₂ + 3H ₂ → CH ₃ OH + H ₂ O ΔH ₂₉₈ = −49.5 kJ / mol (heat generation) (2) For example, Hironori Arakawa Japan Society for the Promotion of Science Coal Utilization Technology No. 14
According to the material of the 8th Committee, 25th Research Meeting, p. 14 (1989), a catalyst system effective for methanol synthesis from syngas also shows a catalytic action for methanol synthesis from carbon dioxide-hydrogen mixed gas. Has been suggested.

[0004]

However, such a conventional proposal has two important problems. First, carbon dioxide-using a conventional methanol synthesis catalyst
When trying to synthesize methanol from a hydrogen mixed gas, the yield of methanol is significantly reduced as compared with the case of using synthetic gas as a raw material. Therefore, it is necessary to improve the conversion rate and increase the yield of methanol for practical use, but it is difficult to achieve a high conversion rate of methanol even if the reaction temperature is simply increased. This is because carbon dioxide is a chemically extremely stable molecule, and from the equilibrium relationship of formula (2), the lower the temperature and the higher the pressure, the higher the methanol conversion rate of carbon dioxide as shown in FIG. is there.
Although it is necessary to lower the reaction temperature in order to increase the conversion rate, doing so slows down the reaction rate and is not practical. Further, there is a problem that the equipment cost of the reactor increases when the pressure is increased.

The second problem is that the economical efficiency of the reaction for synthesizing methanol from carbon dioxide depends on the cost of hydrogen more than ever. In the methanol synthesis from the synthesis gas shown in the above formula (1), all the raw material hydrogen becomes protons constituting methanol, but in the methanol synthesis by the hydrogenation reaction of carbon dioxide, as shown in the above formula (2), 1/3 of the raw material hydrogen is consumed to produce water as a by-product. As described above, since the conversion rate of hydrogen to methanol is worse than that of the conventional one, when hydrogen with high cost is used, the method of synthesizing methanol from carbon dioxide and hydrogen is economically unprofitable. This problem becomes remarkable especially when expensive high-purity hydrogen is used. Therefore, in order to put the method of synthesizing methanol from carbon dioxide into practical use, since the by-product of water is inevitable, suppression of hydrogen cost is the key to practical use. In view of this, it is required to develop a method of using a raw material gas having an inexpensive low-grade hydrogen gas having a low hydrogen content as a hydrogen source.

In view of the above situation, the object of the present invention is to
It is an object of the present invention to provide a method for synthesizing methanol from a low-grade hydrogen gas having a low hydrogen content, such as plant off-gas, as a hydrogen source and using it and carbon dioxide at a higher yield than conventional methods.

[0007]

Therefore, the present inventors have
As a result of repeated research to achieve the above object, the inventors focused their attention on performing a step of reducing carbon dioxide with hydrogen in the presence of a specific catalyst to produce carbon monoxide before the methanol synthesis reaction step. The invention was completed. In order to achieve the above object, the method for synthesizing methanol according to the present invention comprises (a) a metal group belonging to Group IIIb of the periodic table and IVa
Periodic rule is applied to a carrier composed of a complex of an oxide of a metal selected from one or both of the groups of metals belonging to the group and a zinc oxide respectively, or a carrier composed of zinc oxide alone. Table VIII group Ni, Fe, Co, Ru,
Reaction of a source gas containing carbon dioxide and hydrogen in the presence of a catalyst obtained by supporting at least one metal selected from Rh, Pt and Pd and Mo and W of Group VI of the periodic table. And a reaction step of (b) using a methanol synthesis catalyst to synthesize methanol from the raw material gas that has passed through the reaction step (a) by a hydrogenation reaction.

In the reaction step (a), carbon dioxide and hydrogen in the raw material gas mainly undergo a CO ₂ + H ₂ → CO + H ₂ O (3) reverse water gas shift reaction as shown in the following formula (3). In this specification, for convenience,
The reaction represented by the formula (3) is called a reverse shift reaction. The reverse shift reaction (equation (3)) is an endothermic reaction of ΔH ₂₉₈ = 49.5 kJ / mol, and requires heat supply from the outside.

The catalyst used in the method of the present invention uses a gas containing carbon dioxide and hydrogen as a raw material, a reaction temperature of 400 ° C. or higher, preferably in the range of about 500 to 600 ° C., and a reaction pressure of 20 kg / cm ^2. Below, preferably from normal pressure to about 5
Pressure in the range of kg / cm ² and GHSV of about 1000 to 3
The reverse shift reaction of the formula (3) can be efficiently progressed under the condition of 0000 / h. It should be noted that the present catalyst is used after hydrogen reduction at around 300 ° C. to 400 ° C. for several hours or more at around normal pressure before use.

The raw material gas of the method of the present invention needs to contain carbon dioxide and hydrogen, but may further contain hydrocarbons, and as a hydrogen source, for example, exhaust gas from a petroleum refining plant, so-called plant off-gas. Can also be used. Further, even if carbon monoxide is contained in the source gas, it does not adversely affect the reverse shift reaction. It is characterized in that the reverse shift reaction catalyst used in the method of the present invention enables the reverse shift reaction without depositing carbon on the catalyst even if carbon monoxide is contained in the raw material gas. Because. The higher the purity of hydrogen in the raw material gas is, the more preferable it is for the progress of the reverse shift reaction, but the molar amount of hydrogen may be 40% or more with respect to the total molar amount of hydrogen and hydrocarbon. In the reaction system of the present invention, a large amount of C
It is desirable to convert O ₂ to CO. The conversion rate of carbon dioxide defined by the following equation is If it is 15% or more, there is no problem in putting it to practical use, preferably 2
It is 0% or more, particularly preferably 25 to 40%. Conversion, depend H ₂ / CO ₂ ratio in the raw material, H ₂ / C
When the O ₂ ratio is around 3, the conversion ratio is about 30 to 40% at the reaction temperature in the range of 400 to 500 ° C. under normal pressure, which is the upper limit (equilibrium value). When the composition of the raw material is different from this, it can be calculated based on the equilibrium constant (K) under the reaction conditions (temperature, pressure).

The reason why zinc oxide is contained in the carrier of the reverse shift reaction catalyst in the method of the present invention is that the catalyst has a long life due to the sulfur content absorbing effect of zinc oxide. In general,
Even if the raw material gas contains a small amount of sulfur such as H ₂ S as an impurity, it becomes a catalyst poison of the catalytically active portion, deteriorating the catalytic activity and shortening the catalyst life. In this catalyst, most of the sulfur content is absorbed by zinc oxide, so that the catalytic activity does not deteriorate for a long period of time. The content of zinc oxide is generally about 20-100 per weight of carrier.
% By weight. When the content of zinc oxide is about 20% or less, the life extension effect becomes small.

Further, the composite carrier of zinc oxide and the specified metal oxide has the effect of improving the mechanical strength of the catalyst. In particular, in those containing titanium oxide and aluminum oxide, the selectivity of carbon monoxide is improved,
It has the effects of resistance to CO poisoning and resistance to coke formation. If the content of these carrier components is small, the effect of inclusion will be extremely small, and if it is too large, the amount of zinc oxide will be relatively small and the effect of absorbing the sulfur component will be reduced. Therefore, the content of the specified metal oxide is about 40 to 80 per weight of the carrier.
It is preferable to set the weight%. When titanium oxide and aluminum oxide are used in combination, the mixing ratio of both is not particularly limited as long as the total amount of both is within the range of about 40 to 80% by weight based on the weight of the carrier.

The transition metal, which is an active species, may be of any kind, but in particular, a Group VIII metal (especially Ni, F) of the periodic table.
e, Co, Ru, Rh, Pt, Pd) and Group VIa metals (particularly Mo, W) can be preferably used. Each of these transition metals may be used alone, or two or more kinds of metals may be mixed and used. The amount of the transition metal supported (the total amount supported when two or more metals are used) is not particularly limited, but is generally about 5 to 20 per carrier weight.
It is preferable to set it as the weight%.

The reverse shift reaction catalyst used in the present invention is, for example, zinc oxide alone or Group IIIb and VI of the periodic table.
A metal compound selected from group a, for example, one or both of aluminum oxide and titanium oxide is mixed with zinc oxide to prepare a carrier, and the carrier thus prepared is impregnated or coprecipitated with a transition metal by a conventional method. It is prepared by drying, firing, and baking.

When zinc oxide is used alone, the carrier is prepared by calcining metallic zinc in air or by thermally decomposing an inorganic zinc salt (zinc nitrate, zinc borate, basic zinc carbonate, etc.). To be done. In addition, the carrier is Periodic Table II.
In the case of a complex of an oxide of a metal selected from one or both of Group Ib and Group IVa and zinc oxide, the mixing order of zinc oxide and the metal oxide is not particularly limited. For example, as described above, zinc oxide may be mixed with a mixture of aluminum oxide and titanium oxide, or a mixture of zinc oxide with any one of aluminum oxide and titanium oxide. Alternatively, the other may be mixed. Alternatively, a catalyst carrier capable of achieving the above-mentioned intended purpose can be prepared only by mixing a predetermined amount of powder of zinc oxide, titanium oxide, aluminum oxide or the like. A known method such as an impregnation method and a coprecipitation method can be used for supporting the transition metal on the carrier.

As an example of the method for preparing this catalyst, the case where Ni as a transition metal is supported on a carrier of zinc oxide alone is first described. First, zinc oxide is weighed, and water is gradually added dropwise to this to oxidize it. Absorb sufficient water inside zinc. Water absorption
It is necessary to carry out until the inside of zinc oxide is saturated with water. Then, from this saturated water amount and the weighed zinc oxide amount,
Calculate the required amount of Ni and, based on the calculated value, Ni salt adjusted to an appropriate concentration (nitrate, acetate, chloride, etc.)
The aqueous solution may be saturated with zinc oxide, washed, dried, molded, and fired. The same applies to the case of a composite carrier and the case of supporting two or more kinds of transition metals, and the saturated water absorption amount of the composite carrier and the necessary amount of transition metal (the total amount of two or more kinds of transition metals) are calculated. Based on the result, after the saturated aqueous solution of the transition metal salt prepared to have an appropriate concentration is saturated and absorbed, the washing and the subsequent series of steps may be performed as described above.

The reaction process of methanol synthesis has a superficial velocity (SV) of 100 in the presence of a known methanol synthesis catalyst.
0-8000 / h, preferably 1500-5000 /
h, particularly preferably around 3000 / h and a reaction temperature of 2
The reaction is carried out under the reaction conditions of 00 to 400 ° C, preferably 250 ° C to 400 ° C, particularly preferably around 250 ° C. As shown in FIG. 3, the lower the temperature and the higher the pressure, the higher the conversion rate. Therefore, if the reaction temperature is too high, the yield will decrease significantly,
It is not preferable because side reactions such as hydrogenation reaction to hydrocarbon are likely to occur simultaneously. On the other hand, at a temperature of less than 200 ° C., it becomes difficult to activate carbon dioxide and hydrogen on the catalyst even if the conditions are favorable in terms of chemical equilibrium, the reaction rate decreases, and practical use is extremely difficult. It will be difficult.

In the reaction step for synthesizing methanol, the following known methanol synthesis catalysts are used. As the catalyst, for example, Cu-ZnO, Cu-ZnO-Cr
_{2 O 3, CuO-ZnO-} ZrO 2, Cu-ZnO-M
gO, Cu—ZnO—La ₂ O ₃ (for example, Resources and Environment, Volume 3, No. 2, p. 117 (1994), Applied Ca
talysis Vol.4, p281 (1983)) can be used. Among them, a catalyst containing 50% by weight of Cu and 25% by weight of ZnO and ZrO ₂ (for example, resources and environment, Vol. 3, No. 2, p. 85 (1994)), copper nitrate, chromium nitrate, and zinc nitrate were dissolved in water. Ammonia water was added dropwise to make the mixture alkaline to have a pH of 8 to 9 to coprecipitate each hydroxide, and this was baked (for example, Industrial Chemistry Magazine Vol. 70 No. 9, P1473 (1967), Inte.
rnational Journal of Hydrogen Energy, Vol.18,
p. 979 (1993)) can be preferably used. It should be noted that the catalyst used in the reaction step of methanol synthesis is not particularly limited to the above, as long as it has a catalytic performance higher than a predetermined level.

As an example of the method for preparing the methanol synthesis catalyst, commercially available cupric oxide (15 g), chromium oxide (30 g),
After adding water to 105 g of zinc oxide and thoroughly kneading, drying
Mold and fire. Alternatively, dilute aqueous ammonia is added dropwise to separate aqueous solutions of copper nitrate and chromium nitrate to adjust the final pH to 8 to precipitate these hydroxides, which are thoroughly dehydrated at 150 ° C. and dried. 18.5 g of copper hydroxide, 45.6 g of chromium hydroxide and zinc oxide 1 thus prepared
After thoroughly mixing 05 g, water is further added and kneaded, dried, molded and fired. In addition to such a wet mixing method, a known method such as a coprecipitation method may be used. For example, copper nitrate 45.6
g, and 157.9 g of chromium nitrate are dissolved in about 10 liters of water, and 3 to 5N ammonia water is added dropwise to the solution to finish at about pH 8. Next, the formed precipitate is filtered, washed, dried, molded, and then fired. The firing temperature is 500 ° C. to 700 ° C., and it may be performed in air. still,
The above-mentioned catalyst preparation method is an exemplification, and the catalyst usable in the present invention is not limited to the above-mentioned composition and production method.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the accompanying drawings. Exemplary apparatus Figure 1 of the present invention method is a flow sheet showing a schematic configuration of a methanol synthesis apparatus embodying the present invention method. This apparatus is a bench-scale apparatus manufactured in order to demonstrate the effect of the method of the present invention, and a commercial-scale apparatus does not necessarily have to have the same configuration as this flow sheet. As shown in FIG. 1, a methanol synthesis apparatus (hereinafter simply referred to as apparatus) 10 includes a reverse shift reaction tower 12 filled with a reverse shift reaction catalyst, a water separation tower 14, and a methanol synthesis tower filled with a methanol synthesis catalyst. 16, heating furnace 18, first heat exchanger 2
0, a second heat exchanger 22, a cooler 24, and a compressor 26. The heat medium (pure water in this device) is circulated through the heating furnace 18 to heat the stream number in the second heat exchanger 22. Also, pumps and other equipment are omitted.

The raw material gas (stream number) consisting of a mixed gas containing hydrogen gas and carbon dioxide gas is partially used for the quenching of the methanol synthesis tower 16 and heated, and the rest is the first heat. After being preheated by the exchanger 20, they are merged and heated to a predetermined temperature in the heating furnace 18, and enter the reverse shift reaction column 12. In the reverse shift reaction tower 12, a part of the raw material gas is converted into carbon monoxide and water by the reverse shift reaction to become a stream number, and then, after being cooled by the second heat exchanger 20 and the cooler 24, the water is cooled. Enter the separation tower 14. Therefore, the stream number is separated from the water, becomes a stream number, and flows out from the top of the tower. The stream number is further pressurized to a predetermined pressure by the compressor 26 and further heated to a predetermined temperature by the second heat exchanger 22, and then enters the methanol synthesis tower 16, where methanol is synthesized by a methanol synthesis reaction,
It becomes a stream number and goes out of the system.

30 ml (about 24.7 g) of the catalyst prepared as described below is packed in the reverse shift reaction column 12 as a catalyst for the reverse shift reaction. The raw material gas feed rate is set to SV = 3000 to 3300 / h (STP). Titanium oxide powder (TiO ₂ : Degus
sa P-25) 9.8 g, zinc oxide powder (ZnO: Wako Pure Chemical Industries, Ltd.) 5.7 g, aluminum oxide powder (Al ₂ O).
₃ : Aluminum oxide type 1 made by Merck 4.5
20 g of a carrier was prepared by mixing g. Then, nickel nitrate _{(Ni (NO 3) 2 ·} 6H 2 O: manufactured by Kanto Chemical Co., Inc.) 9.
The carrier prepared by dissolving 91 g in 20 ml of water was immersed for 1 hour to remove the residual liquid, dried at 120 ° C. for 12 hours, and calcined at 600 ° C. for 3 hours to obtain NiO; 12.4 wt%, ZnO; 21.3% by weight, balance TiO ₂ and A
A catalyst consisting of l ₂ O ₃ was prepared. On the other hand, in the methanol synthesis tower 16, 30 ml of a methanol synthesis catalyst composed of commercially available Cu—ZnO—Cr ₂ O ₃ (JGC N211B) was used.
(About 28.6 g) is filled.

Example 1 of the Method of the Present Invention Using the apparatus 10 shown in FIG. 1, the method of the present invention was carried out under the conditions shown in Table 1 for each stream number. In this embodiment, the ratio of hydrogen to carbon dioxide as the source gas is 3: 1.
The mixed gas of was used. After reaching a steady state, samples of each stream number were taken and analyzed by gas chromatography. The analytical values of the composition of each stream number obtained are shown in Table 1 in terms of molar flow rate display.

[Table 1]

Example 2 of the method of the present invention In this example, the method of the present invention was carried out under the same conditions as in Example 1 except that carbon dioxide gas and plant off gas obtained at an oil refinery as a hydrogen source were used as raw materials. Was carried out. The analytical values of the composition of each stream number obtained are shown in Table 2.

[Table 2]

Comparative Example by Conventional Method FIG. 2 is a flow sheet showing the constitution of an apparatus for synthesizing methanol from carbon dioxide by a conventional methanol synthesis catalyst. This apparatus comprises a methanol synthesis tower 16 filled with a methanol synthesis catalyst, a heating furnace 18, and a compressor 26. The raw material gas (stream number) containing carbon dioxide and hydrogen was pressurized to a predetermined pressure in the compressor 18, then quenched by quenching the methanol synthesis tower 16, and further heated to a predetermined temperature in the heating furnace 18. After that, it enters the methanol synthesis tower 16. There it is converted to methanol and becomes the stream number. Using the apparatus shown in FIG. 2, the above-mentioned reaction steps were carried out under the conditions shown in Table 3 for each stream number, and used as a comparative example. In this comparative example, a mixed gas in which the ratio of hydrogen to carbon dioxide is 3: 1 is used as the raw material gas, and the analysis value of the composition of each obtained stream number is
It is shown in Table 3.

[Table 3]

In the comparative example, the methanol content at the reactor outlet is about 10.8%. On the other hand, in Example 1,
By installing a high-performance reverse shift reaction tower in the front stage,
About 38% of carbon dioxide is reduced to carbon monoxide, and the outlet gas of the methanol synthesis tower contains about 17% of methanol. Therefore, in Example 1, the conversion of methanol is improved by 160% or more, and the yield is improved by about 30% or more, as compared with the comparative example. In Example 2, 40-60 vol. %, And the plant off-gas consisting of saturated hydrocarbon as the remainder was used, it can be seen that the methanol yield was improved as in Example 1 as compared with the comparative example.
From these results, the process of the present invention, which combines the reverse shift reaction and the methanol synthesis reaction, increases the methanol yield by about 30% or more compared with the current process, and it is possible to use pure hydrogen or plant offgas as the hydrogen source. Methanol can be economically synthesized from carbon oxide.

[0027]

According to the present invention, by using a high performance reverse shift reaction catalyst, methanol can be produced from carbon dioxide and hydrogen in a yield superior to that of the existing process.
Further, as a hydrogen source, a low-grade hydrogen-containing gas, for example, an exhaust gas discharged from a refinery, having a hydrogen content of 40 to
60 vol. Methanol can also be produced in excellent yields using a plant offgas with the remainder being hydrocarbons. Therefore, by adopting the method of the present invention, methanol can be economically synthesized from carbon dioxide and hydrogen, and carbon dioxide can be promoted as a resource.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the constitution of a methanol synthesis apparatus for carrying out the method of the present invention.

FIG. 2 is a flow sheet showing the configuration of an apparatus for synthesizing methanol from carbon dioxide by a conventional methanol synthesis catalyst.

FIG. 3 is a graph showing the relationship between the reaction temperature and the methanol conversion rate of carbon dioxide in the reaction of synthesizing methanol from carbon dioxide and hydrogen.

[Explanation of symbols]

 10 Methanol Synthesizer 12 Reverse Shift Reaction Tower 14 Water Separation Tower 16 Methanol Synthesizer 18 Heating Furnace 20 First Heat Exchanger 22 Second Heat Exchanger 24 Cooler 26 Compressor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/88 X 23/89 X C07C 29/154 29/156 // C07B 61/00 300 (72 ) Inventor Takashi Yoshizawa 1134-2, Gongendo, Satte City, Saitama Cosmo Research Institute Co., Ltd.

Claims (1)

[Claims] 1. An oxide of a metal selected from either or both of (a) a metal group belonging to Group IIIb and a metal group belonging to Group IVa of the periodic table. Ni, Fe, C of Group VIII of the Periodic Table on a carrier composed of a complex of zinc oxide and zinc oxide or a carrier composed of zinc oxide alone.
containing carbon dioxide and hydrogen in the presence of a catalyst obtained by supporting at least one metal selected from o, Ru, Rh, Pt and Pd and Mo and W of Group VI of the periodic table. A reaction step of reacting a raw material gas; and (b) a reaction step of synthesizing methanol by a hydrogenation reaction from the raw material gas that has passed through the reaction step (a) using a methanol synthesis catalyst. Synthesis method.